The zone had four of the largest earthquakes in recorded North American history, with
moment magnitudes estimated to be as large as 7 or greater, all occurring within a 3-month period between December 1811 and February 1812. Many of the published accounts describe the cumulative effects of all the earthquakes, known as the New Madrid Sequence, so finding the individual effects of each quake can be difficult. Magnitude estimates and epicenters are based on interpretations of historical accounts and may vary.
Prehistoric earthquakes As uplift rates associated with large New Madrid earthquakes could not have occurred continuously over geological timescales without dramatically altering the local topography, studies have concluded that the seismic activity there cannot have gone on for longer than 64,000 years, making the New Madrid seismic zone a young feature, or that earthquakes and the associated uplift migrate around the area over time, or that the NMSZ has short periods of activity interspersed with long periods of dormancy. Archaeological studies have found from studies of
sand blows and soil horizons that previous series of very large earthquakes have occurred in the NMSZ in recent prehistory. Based on artifacts found buried by sand blow deposits and from carbon-14 studies, previous large earthquakes like those of 1811–12 appear to have happened around AD 1450 and 900, as well as around AD 300. Evidence has also been found for an apparent series of large earthquakes around 2350 BC. About southwest of the presently defined NMSZ, but close enough to be associated with the Reelfoot Rift, near
Marianna, Arkansas, two sets of
liquefaction features indicative of large earthquakes have been tentatively identified and dated to 3500 and 4800 BC. These features were interpreted to have been caused by groups of large earthquakes timed closely together.
Dendrochronology (tree ring) studies conducted on the oldest
bald cypress trees growing in
Reelfoot Lake found evidence of the 1811–12 series in the form of fractures followed by rapid growth after their inundation, whereas cores taken from old bald cypress trees in the St. Francis sunklands showed slowed growth in the half century that followed 1812. These were interpreted as clear signals of the 1811–12 earthquake series in tree rings. As the tree ring record in Reelfoot Lake and the St. Francis sunk lands extend back to 1682 and 1321, respectively, Van Arsdale et al. interpret the lack of similar signals elsewhere in the chronology as evidence against large New Madrid earthquakes between those years and 1811.
December 25, 1699 The first known written record of an earthquake felt in the NMSZ was from a French missionary traveling up the Mississippi with a party of explorers. At 1 pm on
Christmas Day 1699, at a site near the present-day location of Memphis, the party was startled by a short period of ground shaking. from Devens'
Our First Century (1877)
1811–12 earthquake series •
December 16, 1811, 0815 UTC (2:15 am); (M about 7.5) epicenter in northeast Arkansas, probably on the Cottonwood Grove fault; Local uplifts of the ground and the sight of water waves moving upstream gave observers the impression that the Mississippi River was flowing backwards. :At New Madrid, trees were knocked down and riverbanks collapsed. This event shook windows and furniture in Washington, DC, rang bells in Richmond, Virginia, sloshed well water and shook houses in Charleston, South Carolina, and knocked plaster off of houses in Columbia, South Carolina. In Jefferson, Indiana, furniture moved, and in Lebanon, Ohio, residents fled their homes. Observers in Herculaneum, Missouri, called it "severe" and said it had a duration of 10–12 minutes. :
Aftershocks were felt every 6–10 minutes, a total of 27, in New Madrid until what was called the Daylight Shock, which was of the same intensity as the first. Many of these were also felt throughout the eastern US, though with less intensity than the initial earthquake. In this event, uplift along the fault created temporary waterfalls on the Mississippi River, created a wave that propagated upstream, and caused the formation of
Reelfoot Lake by damming streams.
Modern activity The largest NMSZ earthquake of the 20th century was
a 5.4-magnitude quake on November 9, 1968, near
Dale, Illinois. The quake damaged the civic building at
Henderson, Kentucky, and was felt in 23 states. People in
Boston said their buildings swayed. At the time of the quake, it was the biggest recorded quake with an epicenter in Illinois in that state's recorded history. In 2008 in the nearby
Wabash Valley seismic zone, a similar
magnitude 5.4 earthquake occurred with its epicenter in Illinois near
West Salem and
Mount Carmel. Instruments were installed in and around the area in 1974 to closely monitor seismic activity. Since then, more than 4,000 earthquakes have been recorded, most of which were too small to be felt. On average, one earthquake per year is large enough to be felt in the area.
Potential for future earthquakes In a report filed in November 2008, the U.S.
Federal Emergency Management Agency warns that a serious earthquake in the NMSZ could result in "the highest economic losses due to a natural disaster in the United States," further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Illinois, Indiana, Kansas, Kentucky, Mississippi, Missouri, Oklahoma, Texas, and particularly Tennessee, where a 7.7 magnitude quake would cause damage to tens of thousands of structures affecting
water distribution,
transportation systems, and other vital
infrastructure. The earthquake is expected to result in many thousands of fatalities, with more than 4,000 of the fatalities expected in Memphis alone. The potential for the recurrence of large earthquakes and their effects on densely populated cities in and around the seismic zone has generated much research devoted to understanding the NMSZ. By studying evidence of past quakes and closely monitoring
ground motion and current earthquake activity, scientists attempt to understand their causes and recurrence intervals. In October 2009, a team composed of
University of Illinois and
Virginia Tech researchers headed by Amr S. Elnashai, funded by the
Federal Emergency Management Agency, considered a scenario where all three segments of the New Madrid fault ruptured simultaneously with a total earthquake magnitude of 7.7. The report found that there would be significant damage in the eight states studied – Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and Tennessee – with the probability of additional damage in states farther from the NMSZ. Tennessee, Arkansas, and Missouri would be most severely impacted, and Memphis and St. Louis would be severely damaged. The report estimated 86,000 casualties, including 3,500 fatalities, 715,000 damaged buildings, and 7.2 million people displaced, with two million of those seeking shelter, primarily due to the lack of utility services. Direct economic losses, according to the report, would be at least $300 billion.
Iben Browning's 1990 prediction Beginning in February 1989, self-proclaimed climatologist
Iben Browning, who claimed to have predicted the
1980 eruption of Mount St. Helens and the
1989 Loma Prieta earthquake – predicted a 50% probability of a magnitude 6.5 to 7.5 earthquake in the New Madrid area sometime between December 1 and December 5, 1990. Browning appears to have based this prediction on particularly strong tidal forces being expected during that time, and his opinion that a New Madrid earthquake was "overdue;" however, seismologists generally agree that no correlation exists between tides and earthquakes. This contrasts to the rate of slip on the
San Andreas Fault, which averages up to per year across California. On March 13, 2009, a research group based out of
Northwestern University and
Purdue University, funded by the USGS, reported in
Science and other journals that the New Madrid system may be "shutting down" and that tectonic stress may be accumulating elsewhere. In the November 5, 2009, issue of
Nature, researchers from Northwestern University and the
University of Missouri said that due to the lack of fault movement, the quakes along the faults may only be aftershocks of the 1811–12 earthquakes. According to the USGS, a broad consensus exists that the possibility of major earthquakes in the NMSZ remains a concern, and that the GPS data do not provide a compelling case for lessening perceived earthquake hazards in the region. One concern is that the small earthquakes that still happen are not diminishing over time, as would be if they were aftershocks of the 1811–12 events; another is that the 4,500-year archaeological record of large earthquakes in the region is more significant than 10 years of direct strain measurement. The USGS issued a fact sheet in 2009 stating the estimate of a 7–10% chance of a New Madrid earthquake of magnitude comparable to one of the 1811–12 quakes within the next 50 years, and a 25–40% chance of a magnitude 6 earthquake in the same time frame. In July 2014, the USGS increased the risk assessment for the New Madrid area. ==See also==